I am re-powering my 1988 SUPER SPORT 15 with a 1994 Mercury 60-HP two-stroke-power-cycle loop-induction 60-HP engine with a 1.64 gear ratio.
Q1: what propeller [pitch] is recommended for best overall performance?
ASIDE: the previous engine was a 1990 Mercury 50-HP three-cylinder that is still running well.
1988 SUPER SPORT 15 Re-power
Re: 1988 SUPER SPORT 15 Re-power
Q2: what was the top boat speed with the previous engine?
Q3: what is the engine speed range in RPM that the manufacturer indicates is the optimum engine speed for full-throttle operation?
Q4: what is the amount of change in the total boat weight that will occur when you change to the new 60-HP engine?
Q3: what is the engine speed range in RPM that the manufacturer indicates is the optimum engine speed for full-throttle operation?
Q4: what is the amount of change in the total boat weight that will occur when you change to the new 60-HP engine?
Re: 1988 SUPER SPORT 15 Re-power
With the current Mercury 50-HP engine the best boat speed is 34-MPH.jimh wrote:Q2: what was the top boat speed with the previous engine?
Mercury recommends the full-throttle engine speed be in the rang of 5,000 to 5,500-RPM.jimh wrote:Q3: what is the engine speed range in RPM that the manufacturer indicates is the optimum engine speed for full-throttle operation?
The 60-HP engine weighs about 30-lbs more than the 50-HP engine.jimh wrote:Q4: what is the amount of change in the total boat weight that will occur when you change to the new 60-HP engine?
Re: 1988 SUPER SPORT 15 Re-power
Using the data that existing best boat speed with 50-HP was 34-MPH, I deduce the boat weight using the Crouch Method as 1,561-lbs using a hull factor of 190.
Next I add 30-lbs, set the power to 60-HP, and deduce the new boat speed as 36.9-MPH.
Finally I assume the engine speed will be in the middle of the suggested range or 5,250-RPM, use the gear ratio of 1.64:1, and allow SLIP to be 10. The calculated propeller pitch is then 13.5-inches.
That gear ratio seems rather tall for for a 60-HP engine. Please double check that value.
To estimate boat speed based on power and weight, I use my Crouch's Calculator at
https://continuouswave.com/calculators/crouchCalc.php
To estimate the propeller pitch I use my Propeller Calculator at
https://continuouswave.com/calculators/propCalc.php
Next I add 30-lbs, set the power to 60-HP, and deduce the new boat speed as 36.9-MPH.
Finally I assume the engine speed will be in the middle of the suggested range or 5,250-RPM, use the gear ratio of 1.64:1, and allow SLIP to be 10. The calculated propeller pitch is then 13.5-inches.
That gear ratio seems rather tall for for a 60-HP engine. Please double check that value.
To estimate boat speed based on power and weight, I use my Crouch's Calculator at
https://continuouswave.com/calculators/crouchCalc.php
To estimate the propeller pitch I use my Propeller Calculator at
https://continuouswave.com/calculators/propCalc.php
Re: 1988 SUPER SPORT 15 Re-power
Thank you. I agree on the gear ratio [being unusual], but that is the specification.